A method of forming an annular single-layer ear projecting outward in the radial direction for prevention of dislocation of a poly-V belt at the end of the bottom wall side of the peripheral wall in which poly-V grooves are formed is disclosed in laid-open Japanese Patent Application No. 62-84845.
According to the disclosed method, a cup-shaped blank of sheet metal integrally forming a peripheral wall extending in a direction orthogonal to a bottom wall at an end part of the bottom wall is placed over a circular inner pattern tool for supporting its inner surface, and a V-shaped ear forming protrusion formed on a circular surface of a circular outer pattern tool so as to divide a root part of the peripheral wall into two sections. The peripheral wall corresponds to the thickness range of the bottom wall of the cup-shaped blank, and while rotating, the V-shaped ear forming protrusion is driven into the root part of the peripheral wall and an annular ear is formed projecting outward in the radial direction to prevent dislocation of a poly-V belt at the end of one side of the peripheral wall.
In this ear forming method, however, if the thickness of the bottom wall or peripheral wall is thin, that is, if the wall thickness of the cup-shaped blank is thin, the distance from the bottom of the V-shaped groove formed by driving the ear forming protrusion of the circular outer pattern tool into the root part of the peripheral wall, to the inner surface of the corner part where the peripheral wall and bottom wall intersect becomes extremely short, and this distance becomes even shorter in the subsequent poly-V groove forming step, that is, in the step of forming poly-V grooves in the peripheral wall. As a result, the desired strength cannot be achieved.
Therefore, this ear forming method is forced to use a sheet metal blank of greater thickness, resulting in higher material cost, and a significant increase in weight of the sheet metal made poly-V pulley.
In light of these problems, the present invention is intended to provide an ear forming method for sheet metal made poly-V pulleys, and the poly-V pulleys made therefrom, capable of solving the problems of high material cost and increased weight, while maintaining sufficient distance and strength.